In this type of press, compaction of the material is obtained by kneading, under low static compression, a sample of material contained in a cylindrical mould limited by parallel ends and maintained at constant temperature, to within standardized temperature tolerances.
Kneading by shearing action is provoked by the movement of the axis of the mould which generates a conical surface of revolution with vertex angle 2.alpha. while the ends remain at all times perpendicular to the axis of the conical surface.
The resultant axial force F applied to the ends of the sample, the temperature of the mould and the angle .alpha., are maintained constant for the whole duration of the test. The cross-section and mass of the sample do not vary during the test, but the height reduces continually.
For each sample, the height and the shearing force are measured and memorized as a function of the number of gyrations.
U.S. Pat. No. 5,275,056 and WO 95/22751 disclose gyratory shear presses in which the mould comprises a peripheral ring extending outwardly and maintained between rollers disposed at different levels and driven in rotation about a vertical axis and which ensure tilting of the mould. In these two documents, the means for compressing the material of the sample are arranged above the mould and the latter rests on a fixed table. These arrangements bring about difficulties for replacing a mould containing one sample by a second mould containing another sample, and for making checks on several samples with different parameters, as it is difficult and long to check and change the angle a.
U.S. Pat. No. 5,323,655 discloses a gyratory shear press in which the compression means are likewise arranged above the mould, the latter resting on a rotating table mounted out-of-center on a rotating plate. Here, it is necessary to ensure a relative movement between the lower end of the mould and the rotating table. This is effected by a ceramic disc interposed between the lower end and the rotating table.
In all these documents, the means for compressing the sample contained in the mould are arranged in the upper part of the apparatus, which increases the volume and consequently the mass of the apparatus, and brings about difficulties in positioning the mould before the test and for removing the sample after compaction.
It is an object of the present invention to propose a gyratory shear press which overcomes these drawbacks.